Everything below concerns Sublimation. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Updated 2026-07-02. Numbers and descriptions here follow the published literature rather than marketing material.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and concentrates dissolved solids. Primary drying then lowers chamber pressure so ice changes directly into vapor without passing through a liquid phase. Secondary drying raises the shelf temperature to remove bound water that remains after ice sublimation. The result is a dry, porous structure that can be reconstituted later.
Formulation composition influences whether freeze-drying produces an intact cake or a collapsed mass. Excipients such as sugars and polymers can raise the collapse temperature and provide bulk during drying. The critical temperature for primary drying is often the collapse temperature or the glass transition temperature of the maximally concentrated phase. If the product temperature exceeds this threshold, the frozen matrix may soften and lose structure. Established practice therefore links shelf temperature and chamber pressure to the formulation's thermal properties.
The physics of freeze-drying couples heat transfer, mass transfer, and phase change. Heat supplied through the shelf must reach the sublimation front without melting the ice or degrading the product. Water vapor then travels through the already dried layer and leaves the chamber, where low pressure and cold traps keep it from returning. The dried layer acts as a resistance to vapor flow, so drying rate changes as the front recedes. Open questions remain about how pore structure and formulation heterogeneity affect drying uniformity at larger scales.
The process usually has three stages: freezing, primary drying, and secondary drying. Freezing sets the ice crystal structure and can determine pore size in the final cake. Primary drying removes free ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, although some water may remain as part of the solid. Cycle parameters depend on formulation, fill volume, vial type, and equipment performance.
The physical chemistry of freezing influences whether a formulation forms an amorphous glass or a crystalline solid. Amorphous systems can collapse if product temperature rises above the glass transition temperature of the freeze concentrate. Crystalline systems may show eutectic melting, where ice and solute melt together at a fixed temperature. Formulators add bulking agents, lyoprotectants, and buffers to preserve structure and biological activity. The optimum cycle keeps product temperature below critical thresholds during primary drying while allowing efficient sublimation.
| Property | Value | Notes |
|---|---|---|
| Common name | Freeze-drying | Process removes water by sublimation under vacuum. |
| Typical primary drying shelf temperature | -40 C to -10 C | Set below the formulation's collapse temperature. |
| Typical chamber pressure | 0.05-0.3 mbar | Low pressure allows ice to sublime below its triple point. |
| Water content after drying | 0.5-3% by weight | Higher values may reduce storage stability for some materials. |
| Key thermal parameter | Collapse temperature | Measured by freeze-drying microscopy or differential scanning calorimetry. |
A formulation often contains excipients that protect the active ingredient during freezing and drying. Bulking agents provide structure, while lyoprotectants stabilize sensitive molecules. The freezing step can produce ice crystals whose size and distribution affect the drying rate, and cycle design includes freezing, annealing, and drying phases. If the product temperature rises above a critical value, the cake may collapse or lose its porous structure. Successful lyophilization therefore depends on the interaction between formulation, equipment, and cycle design.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen to convert liquid water into ice. Next, the pressure is reduced below the triple point of water so that ice changes directly into vapor without passing through a liquid phase. This step is called primary drying. The result is a porous solid or cake that retains the original shape of the frozen solution.
After primary drying, secondary drying removes water that remains bound to the material. This stage raises the shelf temperature while maintaining low pressure, which encourages desorption of unfrozen water. Residual moisture can be reduced to a low percentage, improving stability for many products. The process parameters, including freezing rate, shelf temperature, and chamber pressure, influence the final pore structure and reconstitution behavior. Control of these variables helps prevent collapse or meltback during drying.
A typical cycle begins with freezing, which fixes the material into a solid and determines ice crystal size. Primary drying then raises heat under vacuum so ice sublimes, often near or below the collapse temperature of the formulation. Secondary drying removes bound water that remains after ice is gone, usually by gently warming the product. Each stage balances heat input against pressure to avoid melting or structural damage. Temperature probes and pressure sensors guide the transition between stages.
In practice, lyophilization is slower and more energy intensive than simple drying. Cycle times can range from hours to several days depending on load, container, and formulation. Amorphous materials may require excipients that help preserve structure during freezing and drying. The method is widely used for biological materials, pharmaceuticals, and foods where heat drying would cause unacceptable change. Open questions remain about scaling cycles between laboratory and production equipment, and this gap affects technology transfer.
Lyophilization, also called freeze-drying, removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts free water into ice and may also produce a glassy phase. Primary drying then lowers chamber pressure so ice sublimes directly to vapor without passing through a liquid stage. Secondary drying raises the temperature modestly to remove bound water. The result is a porous, dry solid that usually reconstitutes quickly. Each stage influences pore structure, residual moisture, and stability.
The physics of lyophilization depends on phase boundaries and heat and mass transfer. During primary drying, heat supplied to the product must equal the latent heat of sublimation, while water vapor moves through the drying cake to the condenser. If shelf temperature or pressure is set too high, the ice front can exceed the collapse temperature, causing meltback or pore collapse. If conditions are too cold, drying slows and costs rise. Formulation excipients, vial geometry, and freezing rate alter these limits.
From scanning these libraries, the researchers discovered that both DPP-4 and DPP-8 showed a strong preference for breaking down peptides with a proline at the P1 position but they found a great difference at the P2 site; i.e., they found that acidic functionality at the P2 position could provide a greater affinity for DPP-4 over DPP-8. Merck kept up doing even more research and screening. They stopped working on compounds from the α-amino acid series related to isoleucyl thiazolidide due to lack of selectivity but instead they discovered a very selective β-amino acid piperazine series through SAR studies on two screening leads. When trying to stabilize the piperazine moiety, a group of bicyclic derivatives were made, which led to the identification of a potent and selective triazolopiperazine series. Most of these analogs showed excellent pharmacokinetic properties in preclinical species. Optimization of these compounds finally led to the discovery of sitagliptin.
== Further reading == DuBois, Page (1991). Centaurs and Amazons: Women and the Pre-History of the Great Chain of Being. University of Michigan Press. ISBN 0-472-08153-5. Ewans, Michael (2007). Opera from the Greek: Studies in the Poetics of Appropriation. Ashgate Publishing, Ltd. ISBN 978-0-7546-6099-6. ISBN 978-0-7546-6099-6 Gregory, Justina (2005). A Companion to Greek Tragedy. Wiley-Blackwell. ISBN 1-4051-0770-7. Griffiths, Emma (2006). Medea. Taylor & Francis. ISBN 0-415-30070-3. ISBN 978-0-415-30070-4 Hall, Edith (1991). Inventing the Barbarian: Greek Self-definition through Tragedy. Oxford University Press. ISBN 0-19-814780-5. Haralu, L. (2017). Madwomen and Mad Women: An Analysis of the Use of Female Insanity and Anger in Narrative Fiction, From Vilification to Validation. ProQuest Dissertations Publishing. (Accession No. 10643100) Lootens, Barbara J. "Images of Women in Greek Drama." Feminist Teacher, vol. 2, no. 1, 1986, pp. 24–28. JSTOR, JSTOR 25680553. Accessed 27 Mar. 2023. Mastronarde, Donald (2002). Euripides: Medea. Cambridge University Press. ISBN 0-521-64386-4. McDermott, Emily (1989). Euripides' Medea: the Incarnation of Disorder. Penn State Press. ISBN 0-271-00647-1. ISBN 978-0-271-00647-5 McDonald, Marianne (1997). "Medea as Politician and Diva: Riding the Dragon into the Future". In Ckauss, James; Johnston, Sarah Iles (eds.). Medea: Essays on Medea in Myth, Literature, Philosophy, and Art. Princeton University Press. ISBN 0-691-04376-0. Mitchell-Boyask, Robin (2008). Euripides: Medea. Translated by Diane Arnson Svarlien. Hackett Publishing.
Eurogamer echoed criticism on the game's length; reviewer Tom Bramwell commented that "although I'm hard pressed to criticize what you get, the complete absence of everything we've learnt from the likes of Counter-Strike and everything since is frankly bizarre". Bramwell did, however, criticize the game's artificial intelligence and the occasional bug that caused a player to get stuck on a wall. PC Zone's Mark Hill was more lenient, praising the game's artificial intelligence as "intelligent as you could hope an AI enemy to be". In addition, Hill praised the game for showing more activity in the base, noting that "a whole world goes on around you, with people eating at a cantina and scientists doing their laundry. The complex is more alive than ever before". Hill also praised the focus "on a greater interaction with scientists as proper people rather than the two or three models that were cloned throughout the facility who kept repeating the same phrases", describing this as Blue Shift's "greatest achievement". PC Zone's review closed by commenting that "as a Dreamcast extra it works perfectly, but as a standalone PC title there's not nearly enough to it." In his negative review of the game, Jim Preston of NextGen recommended that players play the Half-Life mods They Hunger or Day of Defeat instead. The game sold around 800,000 units at retail, excluding digital sales on Steam.
The cooling trend since the mid-Holocene thermal maximum is consistent with ice core and pollen records, but the corresponding magnitude of cooling is elusive due to complicated influences from local effects such as humidity and soil water composition. The meaning of isotopes in cellulose and its applications is still an area of active study.
Sources: en.wikipedia.org
== Target and function == Heparan sulfate analogues are thought to display identical properties as heparan sulfate with exception of being stable in a proteolytic and glycolytic environment like a wound. Because heparan sulfate is broken down in chronic wounds by heparanase, the analogues only bind at sites where natural heparan sulfate is absent. Also the function of the heparan sulfate analogues is the same as heparan sulfate: structuring the ECM scaffold and protecting a variety of protein ligands such as ECM proteins growth factors and cytokines. By positioning and keeping them in place, in a reconstituted organization mimicking that of before the wound, the tissue can then use these different proteins properly and spatially displayed for inducing cell migration, proliferation and differentiation. This results in improved tissue repair and sometimes a real regeneration process.
=== Combined & global === A different modality is when lysosomes do not just act alone, but in concert with the ER. In this scenario, lysosomes first supply a local, 'trigger' Ca2+ release that then secondarily recruits the IP3Rs or RyRs on the ER by Calcium-induced calcium release (the 'amplifier'). In this mode, lysosomes indirectly evoke a global cytosolic Ca2+ signal (which is actually mediated by the ER). In this way, lysosomal Ca2+ release is amplified, in what is referred to as the 'trigger hypothesis'.
== Proposal of protein primary structure == Hofmeister argued for peptide bonds by process of elimination. C-C, ether and ester bonds were unlikely considering the digestion by trypsin. R=C-N-C=R bonds could be eliminated because it would imply a much larger number of carboxylate groups than is observed experimentally. Hofmeister also argued for peptide bonds based on the biuret reaction observed with all proteins but never with free amino acids. Since biuret has the formula NH2-CO-NH-CO-NH2, that suggested the presence of similar peptide bonds in proteins.
These increases are partially related to the COVID-19 pandemic, which continues to highlight the weaknesses of current food and health systems. It has contributed to food insecurity, increasing hunger worldwide; meanwhile, lower physical activity during lockdowns has contributed to increases in overweight and obesity. In 2020, experts estimated that by the end of the year, the pandemic could have double the number of people at risk of suffering acute hunger, around 130 million more undernourished people. Similarly, experts estimated that the prevalence of moderate and severe wasting could increase by 14% due to COVID-19; coupled with reductions in nutrition and health services coverage, this could result in over 128,000 additional deaths among children under 5 in 2020 alone. Although COVID-19 is less severe in children than in adults, the risk of severe disease increases with undernutrition. Other major causes of hunger include manmade conflicts, climate changes, and economic downturns.
Under the law of July 19, 1871, civil records registered from March 18, 1871, during the Paris Commune, were annulled and rewritten between August 1, 1871, and September 30, 1871, and in the following years. These revised records are referred to as "corrected records" (actes bâtonnés). Only the rewritten records were included in decennial tables, and their dates can differ significantly from the actual events they record. Despite being invalidated by law, the original corrected records remain in the registers and can be searched like any others. At the 12th arrondissement town hall, an accidental fire destroyed birth records from January 1, 1870, to May 25, 1871. These records were reestablished and are classified alongside those reconstructed in the official civil records reconstruction.
Sources: en.wikipedia.org
=== Effects === As with peoples having migrated northward, those with light skin migrating toward the equator acclimatize to the much stronger solar radiation. Nature selects for less melanin when ultraviolet radiation is weak. Most people's skin darkens when exposed to UV light, giving them more protection when it is needed. This is the physiological purpose of sun tanning. Dark-skinned people, who produce more skin-protecting eumelanin, have a greater protection against sunburn and the development of melanoma, a potentially deadly form of skin cancer, as well as other health problems related to exposure to strong solar radiation, including the photodegradation of certain vitamins such as riboflavins, carotenoids, tocopherol, and folate. Melanin in the eyes, in the iris and choroid, helps protect from ultraviolet and high-frequency visible light; people with blue, green, and grey eyes are more at risk of sun-related eye problems. Furthermore, the ocular lens yellows with age, providing added protection. However, the lens also becomes more rigid with age, losing most of its accommodation—the ability to change shape to focus from far to near—a detriment due probably to protein crosslinking caused by UV exposure. Recent research suggests that melanin may serve a protective role other than photoprotection. Melanin is able to effectively chelate metal ions through its carboxylate and phenolic hydroxyl groups, often much more efficiently than the powerful chelating ligand ethylenediaminetetraacetate (EDTA).
The emergence of guerrilla warfare and acts of urban insurrection by the black nationalist parties in Rhodesia allowed racial politics to be elevated into an issue of law and order in white Rhodesian public discourse. To Smith and his government, black nationalists were stateless dissidents whose primary motives were not political, but crime and perpetuating lawlessness; for example, Smith preferred to describe the insurgents as "gangsters" in his commentary. The use of weapons and explosives sourced from communist states by the black nationalists also disguised the racial dynamics of the conflict, allowing white Rhodesians to claim that they were targets of Soviet-directed communist agitators rather than a domestic political movement. Smith and his supporters perceived themselves as collective defenders of the traditional values of the British Empire against the twin threats of international communism, manifested through the Soviet Union's support for black nationalist militants, and the social and political decadence of the West. Often repeated appeals to the Christian heritage of their pioneer ancestors in "defending the free world" and sustaining "Western civilisation" reflected these beliefs. This was hardly an unusual opinion among white minorities in Southern Africa at the time; a dossier compiled by United States intelligence officials on the topic found that:
=== Metals === Pure alkali metals are dangerously reactive with air and water and must be kept away from heat, fire, oxidising agents, acids, most organic compounds, halocarbons, plastics, and moisture. They also react with carbon dioxide and carbon tetrachloride, so that normal fire extinguishers are counterproductive when used on alkali metal fires. Some Class D dry powder extinguishers designed for metal fires are effective, depriving the fire of oxygen and cooling the alkali metal. Experiments are usually conducted using only small quantities of a few grams in a fume hood. Small quantities of lithium may be disposed of by reaction with cool water, but the heavier alkali metals should be dissolved in the less reactive isopropanol. The alkali metals must be stored under mineral oil or an inert atmosphere. The inert atmosphere used may be argon or nitrogen gas, except for lithium, which reacts with nitrogen. Rubidium and caesium must be kept away from air, even under oil, because even a small amount of air diffused into the oil may trigger formation of the dangerously explosive peroxide; for the same reason, potassium should not be stored under oil in an oxygen-containing atmosphere for longer than 6 months.
=== Acute toxicity === Melamine is reported to have an oral median lethal dose (LD50) of 3248 mg/kg based on rat data. It is also an irritant when inhaled or in contact with the skin or eyes. The reported dermal LD50 is greater than 1000 mg/kg for rabbits. A study by Soviet researchers in the 1980s suggested that melamine cyanurate, commonly used as a fire retardant, could be more toxic than either melamine or cyanuric acid alone. For rats and mice, the reported LD50 for melamine cyanurate was 4.1 g/kg (given inside the stomach) and 3.5 g/kg (via inhalation), compared to 6.0 and 4.3 g/kg for melamine and 7.7 and 3.4 g/kg for cyanuric acid respectively. A toxicology study in animals conducted after recalls of contaminated pet food concluded that the combination of melamine and cyanuric acid in diet does lead to acute kidney injury in cats. A 2008 study produced similar experimental results in rats and characterized the melamine and cyanuric acid in contaminated pet food from the 2007 outbreak. A 2010 study from Lanzhou University attributed kidney failure in humans to uric acid stone accumulation after ingestion of melamine resulting in a rapid aggregation of metabolites such as cyanuric acid diamide (ammeline) and cyanuric acid. A 2013 study demonstrated that melamine can be metabolized to cyanuric acid by gut bacteria. In particular, Klebsiella terrigena was determined to be a factor in melamine toxicity. In culture, K. terrigena was shown to convert melamine to cyanuric acid directly.
Sources: en.wikipedia.org
Primary drying removes ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, often under the same vacuum. The two stages differ in the water state being removed.
Freezing determines ice crystal size, pore structure, and the concentration of solutes in remaining liquid. Faster freezing generally creates smaller ice crystals and a denser dried matrix. These features affect drying rate and reconstitution behavior.
Lyophilization reduces water content but usually leaves a small amount of water in the dried material. Some water remains bound to solids or trapped in the dried matrix. Very low water targets can require extended secondary drying, which may alter product stability.
The main change is sublimation, in which ice becomes water vapor without melting into liquid water. This occurs when the chamber pressure is held below the vapor pressure of ice while mild heat is supplied. The result is a dry, porous solid that retains much of its original shape.